1. Field of the Invention
The present invention relates to a measuring instrument, and more particularly to a measuring instrument having a contact piece to be in contact with an object to be measured.
2. Description of Related Art
There has been known a measuring instrument which includes a contact piece to be in contact with an object to be measured, a moving mechanism that moves the contact piece along a surface of the object to be measured, and a controller that controls the moving mechanism (for example, see Document 1: JP-A-2007-309684).
A coordinate measuring instrument disclosed in Document 1 includes a probe (contact piece), a relative moving mechanism (moving mechanism), a controller, and a force sensor (measuring force detector) that detects a measuring force exerted on the probe when the probe is brought into contact with an object to be measured. The controller performs feedback control of the relative moving mechanism based on a deviation of the measuring force relative to a predetermined target measuring force (target value). Accordingly, a surface texture of the object is measured by moving the probe along the surface of the object while keeping the measuring force exerted on the probe substantially constant.
Incidentally, in a typical measuring instrument, when high-speed responsivity is required for a feedback controller such as when a surface of an object to be measured is rugged or when a probe is moved at high speed, the probe is moved away from the object and therefore a surface texture of the object cannot be measured.
On the other hand, since the coordinate measuring instrument disclosed in Document 1 includes a force control compensator for series compensation of a feedback controller, high-speed responsivity of the feedback controller can be improved by increasing a compensation element of the force control compensator.
However, response characteristics of the feedback controller depend on response characteristics of the compensation element of the force control compensator, the force sensor of the feedback controller, the relative moving mechanism and the like. Thus, when the compensation element of the force control compensator is unlimitedly increased, stability of the feedback controller may be impaired.